Students with March for Our Lives pack a hearing of the House Judiciary Committee on gun violence on Feb. 6. (J. Lawler Duggan for The Washington Post)

Today is the first anniversary of the mass shooting in Parkland, Fla., where 17 people were gunned down at Marjory Stoneman Douglas High School. Shortly thereafter, several surviving students began organizing for stronger gun laws around the hashtag #NeverAgain and the organization March for Our Lives.

Many argued at the time that the Stoneman Douglas students’ powerful activism could change the gun debate in ways that other mass shootings hadn’t. And to some degree, they were right.

The surviving students sparked a budding social movement that led over 1 million participants to advocate stronger gun laws at March for Our Lives rallies on March 24. That movement helped lead to 67 new gun-control laws in 2018 — more than triple the number enacted in 2017. And post-Parkland activism is often credited with Democratic politicians’ increasingly vocal support of stricter gun laws.

But, predictably, Parkland’s impact on public support for stricter gun laws has been much less durable.

The graph above shows support for gun control in Civiqs’s daily tracking polls since 2015. Notably, the post-Parkland surge in support for stricter gun laws was larger than it was for more-deadly mass shootings, such as the June 2016 shooting in Orlando, the October 2017 shooting in Las Vegas and the November 2017 shooting in Sutherland Springs, Tex.

Support for stricter gun laws increased by seven percentage points in both Civiqs and Gallup surveys conducted shortly after the Parkland shootings. In fact, the 67 percent of Americans who favored more regulations on the sale of firearms in Gallup’s March 2018 survey represented was the highest in any Gallup poll since 1993.

Yet as with the short-term surges in support for gun control after the school shootings at Columbine High in 1999 and Sandy Hook Elementary in 2012, the Parkland effect on public opinion was fleeting. By the end of 2018, public support for stricter gun laws had returned to pre-Parkland levels in both Gallup and Civiqs surveys.

These results are consistent with one prominent theory of public opinion, which argues that people express opinions based on easily accessible information. In this model, the impact of events such as mass shootings on public opinion persists only so long as the event is in the forefront of the public’s collective mind.

Because media attention to even the most high-profile mass shootings tends to be transitory, so too are these shootings’ effects on public opinion. It will, therefore, probably take sustained media attention to gun violence to create durable shifts in Americans’ support for gun control.